i've been reading this thread all day and i have some comments.
1. you all are making this entirely too complicated. bucket, sand, water flow over top with pump of choice. high flow to keep sediment from forming or use a prefilter. you don't need to know what sand, what bucket, or what pump. just pick whatever you got or whatever you can get your hands on at home depot or lowes
2. the flow through design is crap. a coil denitrator works by having the O2 depleted in the coil and then the denitrifying takes place in the column on the way out. trying to flow through sand will A) have to be really slow, B) have to be really deep, and C) have to be pressurized to get any type of flow. no practical.
3. The other thing about coil denitrators is that their effluent is high in CO2 and thus low in PH. low PH makes aragonite clump and is also bad for a tank if not properly diluted.
4. The flow through to waste is the most absurd idea i've ever heard. what is the point of sending the water through a DSB if you are going to pipe the output to a drain and replace it with fresh water? wouldn't it be more efficient and simpler to just pipe out straight tank water and replace with fresh salt water?
5. nitrates get to the deep sand by way of osmosis. if you don't know how osmosis works, look it up. the short explination is that molecules in an area of high concentration (nitrate in tank water) travels THROUGH water to areas of low concentration (the sand bed). the water does not have to make this journey, the molecules do it on their own through osmosis
6. for those that are implementing a RDSB and doing massive water changes at the same time...consider this. if your nitrates are at 50 ppm and you start a fresh RDSB, the bacteria need time to multiply. if they multiply to a certain point and then you do a 70% water change, the nitrates are now at .3*50=15ppm. the bacteria will now multiply slower because there is less nitrate to support them. however, something in your tank is making nitrates sky rocket, thus nitrates are multiplying faster than the sand bed is seeding. in other words your massive water changes are basically stunting the growth of your sand bed.
i would suggest that if you have massive nitrate problems to put in a rdsb and do regular small water changes (10-20% weekly) so that the nitrates will remain at a constant semi high level while the rdsb seeds but they don't get rediculously high. once the rdsb is running, you should see the nitrates level off. this means that your rdsb is now taking out nitrate at the same rate it is produced, but you've still got that initial high level in there. this is the time to do some huge water changes to get the plateau point down.
i hope that makes sense. if you think about it a little it should. it gives me a headache seeing you all argue in circles and try to base info on other people's experiences when they either didn't give it enough time, were doing something different, or were doing something totally different than what you are trying to apply it to.
1. you all are making this entirely too complicated. bucket, sand, water flow over top with pump of choice. high flow to keep sediment from forming or use a prefilter. you don't need to know what sand, what bucket, or what pump. just pick whatever you got or whatever you can get your hands on at home depot or lowes
2. the flow through design is crap. a coil denitrator works by having the O2 depleted in the coil and then the denitrifying takes place in the column on the way out. trying to flow through sand will A) have to be really slow, B) have to be really deep, and C) have to be pressurized to get any type of flow. no practical.
3. The other thing about coil denitrators is that their effluent is high in CO2 and thus low in PH. low PH makes aragonite clump and is also bad for a tank if not properly diluted.
4. The flow through to waste is the most absurd idea i've ever heard. what is the point of sending the water through a DSB if you are going to pipe the output to a drain and replace it with fresh water? wouldn't it be more efficient and simpler to just pipe out straight tank water and replace with fresh salt water?
5. nitrates get to the deep sand by way of osmosis. if you don't know how osmosis works, look it up. the short explination is that molecules in an area of high concentration (nitrate in tank water) travels THROUGH water to areas of low concentration (the sand bed). the water does not have to make this journey, the molecules do it on their own through osmosis
6. for those that are implementing a RDSB and doing massive water changes at the same time...consider this. if your nitrates are at 50 ppm and you start a fresh RDSB, the bacteria need time to multiply. if they multiply to a certain point and then you do a 70% water change, the nitrates are now at .3*50=15ppm. the bacteria will now multiply slower because there is less nitrate to support them. however, something in your tank is making nitrates sky rocket, thus nitrates are multiplying faster than the sand bed is seeding. in other words your massive water changes are basically stunting the growth of your sand bed.
i would suggest that if you have massive nitrate problems to put in a rdsb and do regular small water changes (10-20% weekly) so that the nitrates will remain at a constant semi high level while the rdsb seeds but they don't get rediculously high. once the rdsb is running, you should see the nitrates level off. this means that your rdsb is now taking out nitrate at the same rate it is produced, but you've still got that initial high level in there. this is the time to do some huge water changes to get the plateau point down.
i hope that makes sense. if you think about it a little it should. it gives me a headache seeing you all argue in circles and try to base info on other people's experiences when they either didn't give it enough time, were doing something different, or were doing something totally different than what you are trying to apply it to.
...).... 
:thumbsup:
